THA Revision - Acetabular Component (Jumbo Cup/Augments)

Indication. Revision of a failed acetabular component where the bone loss is reconstructable with a cementless porous jumbo cup — typically Paprosky Type II and IIIA defects — performed for aseptic loosening, progressive periprosthetic osteolysis, recurrent instability needing a larger effective head, or a failed constrained liner. The defining requirement is that enough host bone remains (about 50 to 60 percent contact) and that both columns are intact. Defects suitable for a jumbo cup: - Paprosky II — moderate bone loss with intact columns, superior migration less than 2cm, cavitary or contained segmental defects, distorted but identifiable landmarks, 40 to 60 percent bone stock remaining.

• Paprosky IIIA — superior migration 2 to 3cm above the obturator line with loss of the anterosuperior or posterosuperior rim, but Kohler's line intact (medial wall competent), the teardrop still identifiable, and less than 50 percent bone stock with the columns still continuous. Absolute contraindications. Active infection (requires a staged protocol), established pelvic discontinuity (Type IIIB — needs a cage or custom implant), superior migration more than 4cm (the biomechanical centre is then too high), non-reconstructible columns requiring structural allograft, or medical unfitness for major revision surgery. Relative contraindications. Severe osteoporosis compromising screw purchase, prior pelvic radiotherapy, neurological disease affecting compliance with protected weight-bearing, severe soft-tissue compromise from multiple prior operations, and the young active patient in whom a biological reconstruction is preferred where possible. The one decision that matters — which defect gets which reconstruction:

Consent specifically for dislocation (the commonest complication), periprosthetic infection, sciatic or common-peroneal palsy, leg-length inequality, re-revision for loosening, vascular injury (rare but catastrophic), heterotopic ossification, and the protected weight-bearing commitment of several months. Preoperative optimization & setup. Exclude infection first — ESR, CRP (and IL-6 if available), with hip aspiration if markers are raised; alpha-defensin if equivocal. Obtain a fine-cut CT (1 to 2mm) with metal-artefact reduction and 3D reconstruction to quantify bone loss, plan cup and augment size, and map safe screw trajectories and the external iliac vessels. Medically optimize (haemoglobin over 110 g/L, albumin, HbA1c less than 7 percent, nutrition) and plan extended thromboprophylaxis for 35 days. Position lateral decubitus for the posterior/posterolateral approach (most common and most versatile), supine for the anterior approach, with all pressure points padded and fluoroscopy available.

The goal is to remove the failed component and all cement and membrane without creating new bone loss, confirm the defect is reconstructable (and not a pelvic discontinuity), restore the anatomic hip centre, achieve a rigid press-fit jumbo cup with 50 to 60 percent host-bone contact and supplemental screws in the safe zones, manage cavitary and segmental defects with graft and augments, and reconstruct with a stable bearing — almost always a dual mobility liner in the revision setting.

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Rehabilitation | Phase | Timing | Weight-bearing & immobilisation | Therapy | |-------|--------|--------------------------------|---------| | 1 | 0 to 6 weeks | Toe-touch (10 to 15kg); strict toe-touch to 12 weeks for protected reconstructions (large defects, augments) | Gait training, active-assisted ROM, isometric gluteals; precautions education | | 2 | 6 to 12 weeks | Partial weight-bearing 50 percent (longer if protected) | Active ROM all planes, resistance bands, pool therapy | | 3 | 12 to 16+ weeks | Full weight-bearing once ingrowth confirmed radiographically | Progressive resistance, gait normalisation, return to ADLs | | Long term | — | Avoid high-impact sport permanently | Annual clinical and radiographic surveillance | Most patients return to desk work by 6 to 12 weeks. Heterotopic-ossification prophylaxis for high-risk patients is indomethacin 75mg daily for 6 weeks OR a single 700cGy radiation dose within 72 hours. Hip precautions. Posterior approach (12 weeks minimum): no flexion more than 90 degrees, no adduction past midline, no internal rotation past neutral. Anterior approach (6 to 12 weeks): no extension past neutral, no external rotation past 45 degrees, no combined extension-external rotation. Thromboprophylaxis. LMWH (enoxaparin 40mg daily) or rivaroxaban 10mg daily for 35 days (extended duration for revision), with mechanical sequential compression until ambulatory; aspirin alone is insufficient for revision surgery. Radiographic monitoring. Immediate postoperative baseline (component position, leg length, any intraoperative fracture), 6 weeks (early subsidence), 12 weeks (confirm stability before weight-bearing progression), 6 months, 1 year, then annually. Red flags: subsidence more than 2mm, progressive radiolucent lines, component migration or rotation, new osteolysis. Complications

Other complications. Heterotopic ossification in 20 to 40 percent (higher in revision, trauma, prior HO — prophylaxis as above; excise if symptomatic and mature beyond 12 months); leg-length inequality (5 to 10mm overlengthening is acceptable for stability, shoe-lift if more than 15mm); chronic pain (exclude infection and loosening first, then multimodal management, gabapentinoids for neurogenic pain); and dual-mobility liner dissociation (rare with modern designs, presents as instability or clicking, needs liner revision).

Why acetabula fail. Aseptic loosening and periprosthetic osteolysis driven by polyethylene wear are the leading reasons for revision THA. Particle debris from the bearing generates a macrophage-mediated inflammatory response that resorbs periprosthetic bone; as bone is lost the cup migrates, the hip centre moves superiorly and medially, and the columns and medial wall may be progressively compromised. The degree and pattern of that bone loss is what the Paprosky classification captures, and it is the single most important determinant of which reconstruction is possible. The Paprosky framework grades the defect on three radiographic signs — the degree of superior migration of the hip centre, the integrity of Kohler's line (the medial wall), and the presence of the teardrop and ischial osteolysis — supplemented intraoperatively by palpation of the columns. The classification is the lens for the whole operation because it dictates whether a biologically fixed jumbo cup is viable or whether the defect has outgrown it.

Key evidence. Paprosky's seminal 1994 paper established the classification and showed that of 147 revised cups only 6 (4 percent) were unstable and all were Type IIIB — adequate host bone is the prerequisite for ingrowth. The jumbo cup's durability is confirmed across series: Lachiewicz and Soileau reported 97.3 percent survival free of loosening at 10 years and 82.8 percent at 15 years (dislocation 9.3 percent the dominant failure, reduced by a head of at least 32mm); Gustke reported 98 percent survivorship at 4 years and 96 percent at 16 years with Harris hip score rising from 44 to 72; and von Roth's twenty-year follow-up showed 88 percent free of aseptic loosening. Sporer and Paprosky defined the limit — once a pelvic discontinuity is present, a trabecular metal cup with augment or a cage is needed, not a hemispheric jumbo cup alone — a message reinforced by Berry's pelvic-discontinuity work (82 percent union with distraction and plating) and Kosashvili's cup-cage series. Guyen established dual mobility as the standard bearing to control instability in revision, cutting redislocation to a fraction.